I've worked with Relocation sellers for over 8 years now. In my experience, you have to offer them something that makes it worth their while to deal with you, as opposed to taking their buy-out. Remember, when they take their buy-out, they generally do not have to worry about repairing any items that come up on a home inspection, which they may have to worry about if they sell to you.
Another strategy you may consider is to work closely with the listing agent to submit an offer the day the buy-out takes place. The transferee's employer does not want to own the house, so they have a vested interest to make a quick deal with you.
Hope that helps!